An optical visual aid is understood by this disclosure to mean, in particular, spectacles with a spectacle lens which is positionable in front of the eye of an observer. However, an optical visual aid within the meaning of the disclosure is also any arrangement of optical elements, positionable in front of the eye of an observer, having at least one spectacle lens or a plurality of spectacle lenses with different optical properties.
A dioptric power component of the dioptric power of the visual aid is understood by this disclosure to mean a contribution of the visual aid in the form of at least spherical power (sphere) and astigmatic power (cylinder and associated axis location) for compensating the refractive error of the observer.
Below, the spherical power (spherical refractive power) of an optical element is specified using the unit [D]=[1/m] (diopter); the astigmatic power (cylindrical refractive power) of an optical element is specified using the unit [DC]=[1/m] and the axis location in degrees.
Within the meaning of the disclosure, a best possible corrective power of a dioptric power component of the dioptric power of the visual aid is understood to mean the property of the dioptric power component that the contribution of the dioptric power component to the dioptric power of the visual aid overall compensates the so-called habitual refraction deficit of the observer at least to ⅕ D, preferably to ⅛ D, of the spherical power, at least to ⅕ DC, preferably to ⅛ DC, of the astigmatic power, and ±5° axis location. The habitual refraction deficit may be ascertained by, e.g., a refraction.
In general, the optician or ophthalmologist creates a prescription with prescription values for a best possible corrective power of the aforementioned dioptric power component of the visual aid.
The partly corrective power of a dioptric power component of the dioptric power of the visual aid is understood by this disclosure to mean the property of this dioptric power component that the contribution of the dioptric power component to the dioptric power of the visual aid overall at least partly corrects the so-called habitual refraction deficit of the observer. A dioptric power component is only partly corrective within the meaning of the disclosure if, on account of the merely partly corrective power, the visual acuity of the observer has been reduced by no more than 0.2 log MAR (Logarithm of the Minimum Angle of Resolution) in relation to the visual acuity obtained by a dioptric power component having a best possible corrective power within the meaning of the disclosure.
The disclosure combines one or more dioptric power components for a best possible corrective power and one or more dioptric power components for a partly corrective power. Here, the partly corrective power may be realized by combining different optical elements in a visual aid or by a single optical element, e.g., a spectacle lens with a dioptric power which is composed of dioptric power components with a spherical power and/or an astigmatic power and/or a prismatic power.
So that an observer is able to see an object arranged in a certain distance region in focus, the object needs to be imaged in focus on the retina of the eyes of the observer. A precondition for this is either that the image produced on the retina lies exactly in an image plane conjugate to the object plane or that the depth-of-field of the image of the object is so large that the unsharpness connected with an imaging on the retina from the image plane conjugate to the object plane cannot be perceived by the observer.
The visual faculty of the human eye is also referred to as visual acuity V. The visual acuity of the human eye is defined as the visual angle, measured in arc minutes, at which an observer is just still able to identify an object with the eye under an aperture angle α of the observation pencil of rays:V:=α/1′
Thus, the eye of an observer with a visual acuity of 1 is just still able to resolve a 1.5 mm large object at a distance of 5 m.
So-called eyesight test devices are used for checking the visual acuity, such as the i.Polatest® eyesight test device or the Visuscreen 500 eyesight test device, both made by Zeiss. Using this eyesight test device, different optotypes in the form of signs embodied as a Landolt ring or as a tumbling E or as numbers or letters with different sizes may be visualized for the eyes of an observer by way of projection onto a display area. U.S. Pat. No. 7,537,343 describes an eyesight test device with a display for displaying optotypes. The different dimensions of the optotypes, which are shown to an observer in the eyesight test devices, in this case correspond to different values of the visual acuity. To test the visual acuity, the optotypes displayed to an observer are reduced in size until the observer can no longer clearly identify the optotypes, but can only still guess these.
The healthy human eye is capable of ensuring sharp imaging on the retina by changing the form of the natural lens of the eye for objects that lie in different distance regions. This ability is referred to as the so-called accommodation capability. With increasing age, the human eye loses the ability of clearly identifying small objects at a short object distance. This is due to the accommodation capability of the human eye reducing with increasing age and hence the eye becomes ametropic for objects lying in the vicinity (presbyopia).
Refractive errors of the human eyes may often be corrected completely, or at least in part, by means of optical visual aids.
The use of an optical visual aid of the type set forth at the outset is known from U.S. Pat. No. 6,089,713. Described therein is a spectacle lens embodied as a progressive addition lens, which has a dioptric power matched to the eye of an observer. Here, this dioptric power of the spectacle lens is composed of a plurality of dioptric power components which belong to different visual zones of the progressive addition lens. This facilitates in-focus vision in different distance regions for an observer, even in the case of a restricted accommodation capability.
US 2009/0210054 A1 describes an optical visual aid with a spectacle lens which has an astigmatism for increasing the depth of field. U.S. Pat. No. 5,557,348, US 2011/0116037 A1, and US 2011/0279912 also disclose such spectacle lenses.
The article “Optimal Astigmatism to Enhance Depth of Focus after Cataract Surgery,” Ophthalmology 98, 1025 (1991) to Sawusch M. R. et al. proposes to provide a positive astigmatism corresponding to the spherical refractive power in intraocular lenses, according to the following relationship:plus cylinder=−sphere−0.25.